Comment 4 for bug 402114

I'm splitting some of the findings out into separate bugs:
  bug #402623 .cix thrashing causes us to re-download the whole index multiple times
  bug #402645 fetch for --2a formats seems to be fragmenting
  bug #402652 smart fetch for --2a does not opportunistically combine groups
  bug #402656 revision texts do not seem to be properly combined into groups
  bug #402657 2a fetch over dumb transport reads one group at a time
  bug #402662 chk groups possibly need more clustering